3.8 MFI slide valve build
 

Hi All -

After more than a few years of collecting parts, I'm finally getting my 3.8 MFI engine built. I talked with Mike Bruns about the build and he agreed to take on my project so I packed my parts in a crate and sent to Florida. My intention was to build something that looks close to a 3.0 RSR engine but with more displacement.

Also, want to mention that Mike has been great to work with as this was a custom build and there were some missing parts and fabrication needed, which Mike handled with no problem as they came up. He also kept me informed with pictures throughout the process.

The engine has recently been built and we have a dyno date at JB coming up soon. I will be uploading some pictures showing the build from the early stages. I'm hoping the engine will produce good power around the RPM range with good AFRs.

Here's some of the build parts and many of you on the forum has helped with obtaining them:

964 CASE (CLEANED AND BLASTED BY EMILE AT EP9)
CASE MACHINE WORK DONE AT OLLIES
964 CAM TOWER
CUSTOM CP PISTON (FRED'S PISTON DESIGN) (11 TO 1)
MAHLE BORE IN 102MM CYLINDERS
GT3 CRANK (CROSS DRILLED AND BALANCED BY CCR)
GT3 MAIN AND ROD BEARINGS
GT3 OIL PUMP
GT3 PANKL RODS - RESIZED BY SUPERTEC WITH NEW ARP BOLTS
SUPERTEC HEAD STUDS
PAUTER ROCKER ARMS
EXTREME HEADS (45/41 PORTS - 53 INTAKE VALVE / 42.5 EXHAUST VALVE)
MFI INJECTOR BLOCKS (RETROSPORT) - MACHINED BY SUPERTEC TO MATCH PORT
SERIES 900 AMBER SHROUD (1969 STYLE)
SLIDE VALVE 46MM - BOUGHT FROM TRE/MITTELMOTOR - SUPERTEC INSPECTED
CUSTOM MFI PUMP WITH MODIFIED SPACE CAM - MFI WERKS
CUSTOM ELGIN CAM - SIMILAR TO GE80
QSC 1.75 HEADERS, Ti GT3 MUFFLER, CUSTOM EXHAUST
CLEWETT SERPENTINE BELT
MSD IGNITION
BLACK MFI HOSES - SUPERTEC
FIDANZA ALUMINUM FLYWHEEL FOR SC & ARP FLYWHEEL BOLTS
911 SC FAN AND HOUSING
SUPERTEC COLD START DEVICE
SUPERTEC RSR PUMP COVER AND BREATHER
RENNLINE VALVE COVERS
JB RACING DISTRIBUTOR



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More Pics of the build

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That looks killer! I love the slide throttles!

What are you going to rev it up to? What fuel are you going to use? What is the expected power? Race car?

Jeeez - engine porn

also - GT3 backbox this thing is gonna be loud lol

Real nice build [emoji106][emoji106]


Sent from my iPhone using Tapatalk

Nice! What cam? Are those stainless valves or Ti?

Standard Xtreme setup is Stainless intake, Inconel exhaust valves. They put what I presume are the same valves (aka GIANT) in some 930 cores I sent them.

The motor should be able to go to 8000 but I want to see what the dyno shows for peak power, it may be lower. For fuel, I plan to use a blend of a racing unleaded with super unleaded. Expected power, I'm hoping for 400, but mainly I want to get good AFRs around the rev range. Mike mentioned on similar engines with PMOs, he can get more than 400. But with MFI, it can take longer to dial it in. Hopefully Mike will chime at some point on that issue, and I'll post the dyno results after the test. For use, I will do some track days with friends, drive on back roads, etc., undecided on racing at this point but it looks fun.

Cam is a custom Elgin (similar to GE80) on a 106 lobe center. The valves are stainless - both intake and exhaust. I discussed Ti with Bill and he thought it was overkill based on expected powerband, etc.

Sounds like a fun engine. The slides should be interesting around town. At a real 11:1 I suspect you will need some racing unleaded to avoid knock or pre-ignition. Are the Pankl rods Ti? 130mm or stock? If Ti and 130mm, you should be able to run at 8000RPM. Once you get the MFI tuned it should be a blast!

We have seen some problems with Pauter rockers failing on 8000 RPM engines. Even the better old style cast rockers have problems up there. My race engine had a cast rocker fail at 8000 RPM and a piece of it jammed up the cam causing it to break between the #4 intake and exhaust lobes. I investigated the Pauter rockers and discovered there were issues.

So, for my new 3.746 (102mm x 76.4mm) build, I ended up going with forged rockers from Hastech in Sweden. I am using Carrillo H-beam rods and custom CP pistons (12.5:1) with William Knight proprietary cams. I have to run 110 to 112 octane leaded fuel. The Xtreme heads are also a custom William Knight setup with stainless intake and Inconel exhaust valves. I am using 48mm AT Power shaftless butterfly ITBs with 1 3/4" custom stainless steel William Knight headers and muffler. A MoTec M150 unit controls the EFI and drive-by-wire setups. The 3.6L version of this made 430 HP. But, it was under-fueled with 45mm ITBs and power peaked at 7400 RPM. With more air and fuel, better headers, and cam timing retarded a bit to favor the top end, I hope to get a bit more power and nice bump in torque.

Looking like a very nice engine plan.
It was a pleasure working with this customer to help make his dream come true.
One of the true benefits of using some of our products is the design features that take them to the next level. One of these design features is the ability to install your piston and cylinder assembly without installing the head studs. In this build, Mike chose the more conventional assembly technique but the ability to install the cylinder/piston combination without dancing around the studs saves hours in build time not to mention the unfettered ease in installing the piston clips.
I look forward to hearing how this project works out. Old school MFI is not cutting edge but it has a cool factor hard to match.

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I would venture 400hp is very do-able with the Xtreme heads. ...that being said, they're motors with EFI, no idea on how well MFI can be tuned.

The engine dyno will be great to see, and then possibly a dyno jet chassis dyno to compare to see what you get for losses engine to wheels.

How much do the pistons and wrist pins weigh, and what are top and second ring thicknesses (all of this except wrist pin weight) is on data you got from CP with pistons.

Yes, the Pankl rods are Ti with 130mm. They have 23mm pins. I was looking for the ones with 22mm pins but the seller didn't have any of those left in inventory so went with 23.

Yeah, unfortunately, I found too late about this. When I told Mike that I had the Pauter rockers, he asked right away when I bought them which was about 4 years ago. He said I should be concerned because Pauter was having coating issues with them at that time. I returned to Brian and he stripped and recoated them. I'm still having second thoughts about the Pauter rockers and may replace to what you have soon. I will need to monitor the wear on these.

I look forward to hearing about your new 3.74 engine, do you think you'll get 30+ more hp compared to the 3.6 version?

The piston weight is 422 grams. Not sure on top and second ring thickness, I sent the box to Mike. I do recall weighing the pins and thought they were heavy, so I bought another set of lighter pins from Jerry at CP (the 23mm pins are heavier), don't have the data on me at the moment.

Did you buy new or use Pankl rods? I know they time out in Cup Car engines and then are often sold to people with no warranty. That seems like an interesting game to play. How many hours will you use them before you get new ones?

Even new Pauter rockers seem to have problems at 8000RPM. If you stay under 7500 RPMs you should be fine. I used to view cast rockers as kind of a fuse for money shifts. As you're more likely to break a cast rocker than have a valve bend badly or break which is clearly more catastrophic than a broken rocker. A money shift with forged rockers is a real money shift! I feel fine using forged rockers now as I am using a sequential gearbox with paddle shift. A money shift is now all but impossible.

No, I don't think we will see a 30 HP gain. The displacement increase is only 4.1% so a 17HP gain would be the most I would expect all other things being equal. I hope for a little more than that as we do have more appropriately sized ITBs and better headers. I am expecting the bigger gains to be on the torque side of things.

I'll try to remember to PM you with the results I get from the engine when it is tuned.

Like the motor!
Mike gets 400+ hp a 3.6 on carbs, so with Xtreme heads on MFI I’d think you’ll be in that range as well.
I’d have to agree on the wariness on those rockers too. For the motor specs you describe, I understand many builders prefer stock rockers for the reason winders mentioned. In an overrev situation, you have a chance of just breaking a rocker if there’s any piston to valve contact, and that’s is easy to replace. I’m about to assemble a 3.5 with similar specs to yours (no Xtreme heads though) and opted for the stock rockers. Carbs for now but planning to go MFI at some point. I’m doing vintage, so slides would be cool.

I'm curious about the choice of Slide valve intake. Can you talk about the reasons and expectations for non-race application? Did Supertech do any work on the unit, Mittlemotor pieces seem to have had a lot of quality issues.

Over the last 40 years when we were looking for reliable rockers for an 8000 RPM engine our go to rocker were forged RSR rockers. They have become crazy expensive and they are a challenge to adjust. You need a large assortment of lash caps and changing them means sliding the rocker shaft out.
The next best option has always been the early adjustable forged rockers that came in early 911 2.0 engines.
They have been replaced over the years to alleviate the "money shift" issue but for those who prefer something special, these are it.
The early rocker has a slightly better ratio 1.5:1 vs 1.45:1, they a lighter 110grams vs 135 and they don't break.
From the factory the contact pad has a chrome face for reduced friction and long life.
When we rebuild them, strip the chrome, we replace the bronze bushing with our proprietary DP4 bushing, surface the pad relative to the new bushing, and a chromium layer of 60 to 80 μm is used.The chrome is then polish to an RA of .2 and blasted with low pressure media and dry film coated.
The obvious problem is the limited supply. We have a few sets on the self but we keep looking.
The friction reduction of the DP4 bushing is maybe the most beneficial change. We believe that this simple improvement may be worth 5 hp and reduced heat in the top end.

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From the LN Engineering website:

Hastech Engineering's Porsche 911 & 964 forged rocker arms are a drop in replacement for stock rocker arms. Unlike stock cast rockers, these will not break if you have an over-rev or if used in an engine that will see high rpm use above 7400 rpm. Hastech forged rocker has a long pad follower and is based on the design used by Porsche for their forged rockers used in early 911 engines. These rockers enable the use of higher lift performance camshafts and also feature high strength bushings and DLC coating for low friction and long life. Hastech has used these rockers in all their race engines for years and are recommended for all aircooled Porsche 911 engines for both street and track.

Additional information from the Hastech website:

Drop in replacement for stock rocker arms
Will not break like stock cast items.
Steel forging to early 911 shape
Long pad follower
OEM Swivel foot
Weight incl Swivel foot, 125 grams
Enables use of new generation higher lift camshafts
DLC coated with high strength bushing
Race proven for many years

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